JP2007519959A - Bifocal contact lens - Google Patents

Abstract

  A contact lens having a near vision portion and a far vision portion, the first position corresponding to aligning the wearer's gaze through the near vision portion on the eye, and the wearer's gaze at the far vision portion A lens that can be moved between a second position corresponding to alignment through. The lens is positionally stable on the eye in each of the two positions and requires a force to be applied to the lens in order to move between the first position and the second position. Preferably, the lens has a back surface and a front surface, the back surface having one or two main back curve zones that occupy a major portion of the lens back surface.

Description

The present invention relates to contact lenses, and more particularly to bifocal contact lenses in which at least one primary and secondary optical zones are present.

Background of the Invention A bifocal lens typically consists of two or more zones or zones with different optical powers, including a distance power zone for distance vision and a near power zone for near or close range vision. ing. The two zones can also be subdivided into further power zones, in which case the lens can be referred to as a multifocal lens.

  The retinal image and the resulting visual perception depends on the light entering the eye through the entrance pupil. In order for a bifocal contact lens to function properly, the entrance pupil is at least partially or more effectively completely covered by the lens's distance vision zone when the eye is looking at a distant object, and the eye is in close proximity. Must be completely covered at least partially or more effectively by the near power zone of the lens. This feature causes a shift (typically vertical) or translation of the contact lens when the eye sees distant and nearby objects alternately, with one or the other zone in front of the entrance pupil. This can be achieved by the principle of alternating vision to be arranged.

  This is known as simultaneous vision, in which the lens is designed and mounted in such a way that some or all of the far and near power zones are placed in front of the entrance pupil at the same time, each contributing to the retinal image simultaneously. Alternative principles can also be used. This type of lens does not require translation, but has the disadvantage that two images can be seen simultaneously. Although the present invention is not related to non-translating lenses, translation may be combined with simultaneous vision.

  In the rigid prism bifocal contact lens, the lower edge of the lens tends to be on the upper edge of the lower eyelid. When the wearer sees a distant object, the distance power zone is ideally positioned to cover the entrance pupil of the eye, and the near power zone is positioned below the entrance pupil. The lens is held in place by gravity and downward force on the upper eyelid. For close looking tasks, the eye rotates downward and the contact lens ideally shifts upward relative to the eye, moving the near power zone to the frontal position of at least part of the entrance pupil, Provide optical correction for near vision.

  Attempts have been made to design soft contact lenses that operate in a manner similar to the hard lens method described above. However, bifocal soft contact lenses are much larger than hard contact lenses, usually 13 to 15 mm in diameter, and often tend to cross the eye ring. When a soft prism bifocal contact lens is worn, the thicker part of the lens moves down and is located under the lower eyelid. As a result, the lens is not supported and pressed down by the upper edge of the lower eyelid. Thus, the prism component can move the prism bifocal soft contact lens to the desired low position and control the rotation in the meridian direction, but the eyes point back and forth between a distant object and a nearby object. When changing, a vertical lens shift cannot be induced.

  Currently available bifocal soft contact lenses do not provide sufficient vertical shift movement to satisfy the alternating vision principle, and therefore do not provide acceptable vision for both distance and near vision. Most bifocal soft contact lenses available today are of the concentric bifocal type and operate on the principle of simultaneous vision. These lenses do not provide good vision at both distance and near vision and are only satisfactorily worn by those who may accept less than optimal vision.

  Devices for inducing vertical shifts in bifocal soft contact lenses are known. U.S. Pat. No. 6,109,749 describes a bifocal soft contact lens having an integrally molded bevel to assist in translation of the lens. The slope has upper and lower shoulders that converge to form an extended slope. The slope does not form part of the optical part of the lens. US Pat. No. 5,635,998 shows a multifocal contact lens having an ellipse and a prism, which combine to create an elongated contact zone between the base portion of the prism and the lower eyelid. Yes. U.S. Pat. No. 5,912,719 shows a lens composed of an eyelid boss that protrudes locally from an outer surface in the peripheral direction and has a ridgeline of limited dimensions. The ridge has a peak in the middle area.

  U.S. Patent Application No. 20030161631 discloses a bifocal soft contact lens that includes two or more prisms that cooperate but differ in structure and function in the same lens. One of the main prisms provides the desired lens vertical placement during distance viewing and control of the meridional rotation around the cornea, i.e. the annulus. In addition, a secondary prism extends forward from the adjacent lens surface to provide a vertical lens shift, or translation, so that the desired optical power zone of the contact lens is in front of the eye entrance pupil at the desired timing. It has a base that allows you to move to. Typically, a lens includes a segmented bifocal zone on one face with the lens's far vision power zone located at the top and the near vision power zone located at the bottom.

  Thus, for use with both soft and hard bifocal contact lenses, the lens is automatically translated so that the desired optical power zone of the lens is in front of the entrance pupil of the eye at the desired timing. Devices for this are known. However, one problem with translational bifocal contact lenses is that in the absence of external forces, such as those caused by eyelid interference, the lens attached to the eye will try to move to a position of minimum potential energy. This process is generally called “centering”. The potential energy is, in the sense used herein, determined by a combination of gravity, internal elasticity, surface tension, pressure / aspiration under the lens and lens / tear film / eye interaction. The influence from the interaction with the eyelid is excluded from the concept of potential energy.

  Lens translation or displacement is a three-dimensional quantity (x, y and rotation) that is further complicated by lens distortion, but for the purposes of this specification, unless otherwise noted, it represents a one-dimensional variable (generally representing vertical displacement). ).

  In order to displace the lens from the minimum energy position, it is necessary to apply an external force. The displacement increases the potential energy of the lens, and when the displacement force is released, the lens attempts to return to the minimum energy position, i.e., center itself again. Ideally, the lens optics is tuned to shape so that this minimum energy position provides the desired optical correction. Of course, in the translating bifocal contact lens discussed above, the lens will correspond to two positions that must provide the desired optical correction: one position corresponding to near vision and distance vision. Has one position.

  In prior art lenses, at one or the other of the positions, the lens is not in its minimum potential energy position. Holding the lens away from its minimum energy position requires an externally applied force, such as the presence of an interaction with the eyelid, that is maintained while the lens must remain in this off-center position. It must be. The application of this force can cause discomfort and mechanical injury to the delicate structure of the eye.

  Furthermore, variations in the position of the eyelids can change the force acting on the lens and thus change its position on the eye, which can interfere with optical performance.

In accordance with the present invention, a contact lens having a near portion and a far portion, a first position corresponding to aligning a gaze of a wearer through the near portion on the eye; Can be moved between a second position corresponding to aligning the wearer's gaze through the distant portion, positionally stable on the eye at each of the positions, A contact lens is provided that requires a force to be moved between a position and the second position.

  Further, the lens has a back surface and a front surface, and the back surface has one or two main back curve zones that occupy a major portion of the lens back surface. Together, the main parts can constitute at least 50% of the back side. In some cases, the peripheral edge of the lens does not form part of the main back curve zone.

  In some cases, the back surface is defined by a major and minor (minor) concave surface and may further include a blend zone that folds well with these concave surfaces. The shape of the back is preferably adapted to the continuous second derivative. More preferably, the shape of the back is adapted to an infinite continuous differentiable function. In some cases, the peripheral edge on the back of the lens does not form part of the large or small surface.

  An alternative is that at least the center of the back of the lens comprises a concave surface or a combination of two concave surfaces, i.e. any two points on one such concave surface between the points of the lens. It can be connected by a straight line that does not pass through the interior. In some cases, the concave surface covers the entire back surface of the lens, but its peripheral edge may not form part of the concave surface. These concave surfaces can be combined with a narrow blend zone (perhaps not itself concave) to achieve continuity at the joint.

  The lens can be positionally more stable at one position than the other position, and therefore when moving from a stable position to an unstable position, the lens is moved in reverse Requires more power than

  The lens can be a soft lens, and the cross-sectional shape can change when moving between the first position and the second position. Partial inversion of the lens can occur during the change in cross-sectional shape. Unless otherwise noted, a lens “shape” as used herein refers to a “static shape”, ie, a shape that minimizes internal stress.

Detailed Description of Embodiments Referring first to FIG. 1, it is noted that the center position of the lens on the eye, indicated by reference numeral 10 on the graph, is the minimum potential energy position. Movement of the lens away from this position in either direction increases the potential energy of the lens, and therefore some form of external force is required to hold the lens at a higher potential energy position.

  On the other hand, FIG. 2 shows two low potential energy points on the graph, indicated by reference numerals 12 and 14. These two low potential energy points correspond to the position of the lens on the eye corresponding to the optimal position of the contact lens in near and far vision according to the present invention. In some cases, one of these positions is at a lower potential energy than the other position, making the lowest potential energy position more stable and making it difficult to accidentally leave that position. For safety reasons, it is important that the lens does not accidentally move from the far vision position to the near vision position. In many situations, such as driving a car, accidental movement of the lens from the far-sighted position to the near-sighted position can lead to potentially dangerous situations and can make it difficult to leave the far-sighted position. Reduce the risk of this occurring.

  Between the near and far vision positions, there is a slightly higher energy position, indicated at 16, which may conveniently be referred to as a “detent” position. The force used to translate the lens from the near vision position to the far vision position and vice versa must be sufficient to push the lens over the detent position 16. After that position, the lens should slide into the other low energy position under the influence of its potential energy. Note that the transition between the two low energy positions is relatively smooth to ensure that no mechanical damage to the eye surface occurs during translation. The energy curve outside the two low energy positions is relatively steep, as shown at 18, ensuring that the lens translation only occurs between the two low energy positions.

  A typical bifocal soft lens 20 of the present invention is shown in FIG. As shown, the lens includes a peripheral region 22 and a central region 24. The central region is divided into two zones: a far vision zone 26 and a near vision zone 28 located below the far vision zone. The two zones are separated by a junction 30. The entrance pupil of the eye, indicated by dotted line 32, is typically aligned with the distance portion of the lens and is centered with respect to the geometric center of lens 20. The lens 20 has a ledge or prism 34 with which the upper edge of the lower eyelid engages to translate the lens.

  Another type of lens not shown is similar to that described in U.S. Pat. No. 6,109,749 which discloses an integrally molded ramp with which the lower eyelid engages to translate the lens. Also good. Other types of translation mechanisms are described below. In other words, the mechanism for translating the lens between its near and far viewing positions may be of the type shown in this patent specification or is referenced in the background section of this specification. It may be of the type shown in other specifications.

  A lens 40 having an inner surface 42 with two dimples or convex portions 44 and 46, each corresponding to a position of minimum energy, is shown in FIG. By translating the lens upward from the position shown in FIG. 4A to the position shown in FIG. 4B, the lens moves from the far vision position to the near vision position. It will be appreciated that great care must be taken regarding the inner shape of the lens between the two stable positions in order to avoid mechanical damage to the eye when transitioning between the two positions. This may be accomplished, for example, by providing a blend zone (not shown) in between to smooth the joint. As mentioned earlier, it is important to avoid accidental transitions from far-sighted to near-sighted positions that can be dangerous in driving and other situations where accurate distance is important. This can be achieved by making the far vision position a lower energy position than the near vision position. Such lenses can also have a peripheral zone (not shown) to improve the overall compatibility with the eye shape.

  A different mechanism for achieving a bistable contact lens structure is shown in FIG. FIG. 5A shows the undeformed lens 50 before being worn on the wearer's eye. In this case, except for the peripheral zone (not shown), the back surface of the lens forms one concave surface, but the same mechanism may be used for other back shapes. The lens 50 can be deformed by reversing either the bottom of the lens recess or the top of the lens, as shown in FIGS. 5B and 5C, respectively. Note that in the illustration of FIG. 5B, the lower portion 52 of the lens is inverted in the upper ring region of the eye 54, and in the illustration of FIG. 5C, the upper portion 56 of the lens is inverted and fits in the lower ring portion of the eye. I want. It is clear that the illustration in FIG. 5B shows the position of the lens in the near vision, and FIG. 5C shows the lens position in the near vision.

  It will be appreciated that the present invention eliminates the need to use the eyelids or other mechanisms in the eye to maintain the lens in a fixed position, i.e., either a near or far vision position. It is envisioned that this significantly reduces the discomfort and deleterious effects associated with constantly maintaining the lens in a non-minimum energy position. Avoid current methods for holding the lens in one of these positions, ie, providing a ledge on the lens or cropping the lens to achieve the required interaction, thereby minimizing discomfort And the production of the lens is supported. Since the present invention requires only a transient force to translate the lens, the ledges, bevels or other features can make the overall dimensions smaller, and possibly none at all.

  Another use of the lens may be for purposes other than bifocal vision correction. For example, a lens with a colored upper half and a transparent lower half allows the wearer to block dazzling sunlight outdoors and then switch to a transparent part of the lens for indoor use Will.

  As previously mentioned, the back surface of the contact lens, i.e. the surface in contact with the sensitive tissue of the eye, must be configured to minimize mechanical damage or irritation to the eye.

Examples of lens shapes and other features include:
1. The back surface may be generally concave. That is, any two points on the back surface can be connected by a straight line that does not pass through the inside of the lens between the two points.

2. The back surface may be formed of multiple regions, each individually concave.

3. The back surface may be similar to 2 above but may include a non-concave blend zone between the concave zones.

4). The back surface may be similar to 1, 2 or 3 except for the peripheral part of the lens.

5. The back surface may have an infinite continuously differentiable function shape. Such a shape would be defined by a single mathematical function. Such a surface will typically be smooth to allow undamaged translation.

6). The back surface may be similar to the above 5 except for the peripheral portion of the lens.

7). The back surface may have a shape defined by a continuous second derivative rather than an infinite continuous differentiable function.

8). The back surface may be similar to the above 7 except for the peripheral portion of the lens.

9. The back surface, as in 1 or 4 above, may be stationary and generally concave, but the lens itself may be deformable at different positions on the eye.

10. The back surface may be formed to better match the shape of the eye at its intended stable position than at its intermediate position.

11. The back surface may be configured to fit a “compound eye” shape (FIG. 6) that represents a combination of two or more different eye positions relative to the lens, thereby providing a good fit to the eye at these positions. Good.

12 The back surface may be generally shaped like 10 or 11 above, but a blend used to smooth the lens area may also be used. Otherwise, the lens will experience a sudden change in curvature.

13. The back surface may be shaped as described above 10, 11 or 12, but may have different orientations caused by rotating the eye shape vertically about the scleral center of curvature (thus, hence If the sclera is nearly spherical, it is possible to use the same scleral curve at both positions).

14 The back surface may be shaped as described above 13, but there may be a difference in rotation between different eye orientations to match the desired lens translation distance (determined by the eye and other characteristics). .

15. The back surface may be shaped as in any of the above, but the lens may be stabilized against rotation about the central axis of the eye (eg by prism ballast or other method).

16. The lens can be manufactured as follows.
First, four kinds of precursor shapes are defined.

Shape 1
Approximate eye shape composed of a spherical sclera and an elliptical cornea with the cornea facing forward. In the most preferable embodiment, the corneal center radius is set to 7.8 mm, and the cornea P value (“Guillon, M., Lydon, DPM, and Wilson, C. (1985) Corneal topography: a clinical mode. Ophthalmol. Physiol. Opt. ., 6, 47-57 ”) is set to 0.75, the cornea diameter is set to 12.5 mm, and the scleral radius of curvature is set to 12.0 mm. Is used. Alternatively, these parameters may be determined by reference to the individual patient's eye shape (FIG. 7a).

Shape 2
Similar to shape 1, but rotated around the center of the scleral sphere and raised the apex of the cornea by a distance T / 2 (T is the desired translational distance for that lens). (The most preferred value of T is 3.7 mm. Alternatively, T may be determined by reference to individual patient eye dimensions and other clinical factors) (FIG. 7b).

Shape 3
Similar to shape 1, but rotated around the center of the scleral sphere to reduce the apex of the cornea by a distance T / 2 (FIG. 7c).

Shape 4
A shape resembling an eye with two corneas by overlapping shapes 2 and 3. Depending on the size of the cornea and the distance T, these two corneal zones may abut (in which case they are truncated accordingly (FIG. 8a)) or may be separated (FIG. 8b).

  Next, three zones in shape 4 are defined (FIG. 9).

Zone 1
The region corresponding to the “upward” corneal region (if it meets the “downward” region, its intersection is truncated).

Zone 2
The region corresponding to the “downward” corneal region (if it meets the “upward” region, its intersection is truncated).

Zone 3
The sclera outside of zones 1 and 2.

  Next, select a lens circumference that is wide enough to be located in zone 3 and completely surrounds zones 1 and 2. In the most preferable example, the circumference is a circle having a diameter of 16.7 mm, and the center is located on the central axis of the shape 1. Non-circular and / or offset perimeter shapes may be used.

  In this way, a preliminary back shape is defined. Once bounded by the selected perimeter, it will conform to shape 4 within that perimeter. The result is a spherical surface (sclera curve) that is cut between two “dimples” that are upward and downward and conform to the shape of the cornea (FIG. 10).

  A “blend region” is identified that covers the area where each zone meets each other. In the preferred form, this zone covers all points within 0.25 mm from these boundaries. Other values may be used as appropriate for the overall lens size and steepness of the joint (FIG. 11).

  Next, the preliminary back shape is deformed in the blend region to smooth the transition between zones 1, 2 and 3. Any method that provides a smooth transition from one zone to another may be used (eg, spline fitting, repetitive or non-repetitive filtering methods).

  The resulting shape with the blend portion smoothed forms the back of the lens. It will be appreciated that the lens can be moved vertically between two stable positions. In one position, the lens closely fits the eye shape in both Zone 1 and Zone 3, and in the other position, the lens closely fits the eye shape in both Zone 2 and Zone 3. At the intermediate position, only the shape of the eye in zone 3 is adapted and its stability is reduced.

  The front surface of the lens is then formed according to the optical and other requirements of the lens. In some cases, prisms (increasing thickness towards the base) are used to provide rotational stability or to help cause transitions between lens positions. Next, in some cases, the edge of the lens may be tapered. In the prototype, the lens was set to a constant thickness of 0.100 mm, or set to a gradually increasing thickness from 0.100 mm at the top of the lens to 0.300 mm at the bottom of the lens (most preferred). These prototypes included a 0.5 mm wide taper zone around, with the width smoothly tapering to reach 0.080 mm at the edge of the lens (FIG. 12).

17. The lens may have the same shape as any of 11 to 16 above, but the back surface may be “straightened” so as to form one concave surface (FIG. 13).

18. The lens flips each region of the lens from one stable point to another as part of the transition, allowing a good fit at any such position, but not between them Such a shape may be used (FIG. 5).

19. The lens can be manufactured (possibly in combination with a shape effect) such that the regional stiffness difference produces or assists in generating a large number of stable points.

20. The above 19 can be achieved by changing the lens thickness for each region.

21. The above 19 can be achieved by changing the composition of the lens material for each region.

22. The above 19 can be achieved by changing the treatment applied to the lens from region to region (eg, thermal, chemical or photochemical treatment).

23. The shape effect can be enhanced by prestressing the lens material (eg thermal, chemical or photochemical treatment).

24. The shape effect can be enhanced by the surface tension effect on the fit of the lens edge to the eye shape.

  Once the lens shape has been defined using the techniques discussed above, lens manufacture is performed using typical lens manufacturing techniques. Such techniques are well known in the art and need not be described in detail herein. Contact lenses can be made from a wide range of materials (eg, hydrogels, silicone hydrogels) and can be subjected to a variety of surface treatments (eg, plasma coating, antimicrobial coating). The choice of materials and surface treatment is primarily determined by taking into account other issues not directly related to biocompatibility and the mechanical behavior of the lens. Since the choice of material affects the refractive index of the lens, the intended material is considered when designing the lens shape and the final shape should satisfy both bistability and desired optical properties. One approach to achieving this result is to start by determining the back shape that leads to the desired mechanical behavior (including bistability in this case) and then combine it with the determined back surface to achieve the desired optical correction. An iterative or other method is used to calculate the frontal shape to provide. In doing so, it may be necessary to take into account the fact that the lens deforms from its “static shape” when it is attached to the eye.

  Once the back and front surfaces are determined, a physical lens can be manufactured with a central thickness. This is typically done by calculating a number of points on each surface, thereby obtaining an approximation of those surfaces and providing that data to a computer driven manufacturing tool (eg, a lathe). Then, using this data, a master (generally made of high-grade steel) is cut into a desired lens shape, and the master is used to manufacture a mold in which the lens can be molded. Alternatively, the data may be used to cut the front and rear halves of such a mold, or the data may be used to cut the lens itself. Alternatively, the master, mold or lens itself can be made using computer driven deposition techniques. Many contact lenses are made of a dehydrated material and then hydrated prior to use, but hydration generally causes considerable swelling of the lens material. Therefore, it may be necessary to adjust the lens shape data to account for this expansion so that the final product has the desired dimensions. It may also be necessary to polish the master, mold and / or lens. Other techniques, such as milling, grinding, cutting, etc. may be required to achieve a specific lens shape.

  It will be appreciated that in order for a wearer to obtain the benefits of a bifocal lens of the type described herein, the lens must be able to translate between its two stable positions. “Parallel movement” refers to movement of the lens relative to the eye. This parallel movement may be in the horizontal direction or in the vertical direction. However, the concept discussed here can also be applied to rotation of the lens about the central axis. The exact manner in which the translation occurs is naturally dependent on the lens structure, particularly the shape of the back surface. To achieve the necessary translation, a translation mechanism, such as an integral ledge or bevel that contacts the eyelid as the eye moves, can be used.

  With normal contact lens wear, a certain amount of translation caused by events such as blinking or eye movement is natural. Moderate translation during blinking may be desirable because it helps remove necrotic cell debris from under the lens, but the inability to re-center quickly after excessive translation or blinking is uncomfortable. This is undesirable because it may cause it to interfere with the optical performance of the lens.

  A bifocal lens of the type discussed herein is intended to shift the lens between two gaze positions (typically “near vision” and “far vision”) with respect to the corresponding optical zone on the lens. Depending on the translation achieved. This may be achieved by applying force to the lens. For example, when the wearer looks down, the lower edge of the lens touches the lower eyelid to displace the lens, or the wearer may manipulate the lens by other methods (eg, by hand). When such a force is applied, all lenses translate. The purpose of bistability is to maintain a constant translation even when the force is released, compared to conventional lens designs that attempt to return to a single “centering” position when no external force is present. It is.

  As used herein, “bistable” or “bistable” means that the lens has the property of being stable at two positions on the eye.

  The invention described herein has been specifically described in connection with a bifocal lens. However, it will be appreciated that the disclosed concepts are equally applicable to multifocal lenses or other types of translating lenses.

  It will be understood that the invention disclosed and defined herein also includes within its scope all alternative combinations of two or more individual features that may be apparent from the foregoing or the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

  Although the embodiments of the present invention have been described so far, modifications obvious to those skilled in the art can be added to the present invention without departing from the scope of the present invention.

1 shows a graph plotting potential energy versus displacement for a prior art contact lens (not proportional to original size). A similar plot of a contact lens of the present invention is shown (not to scale). FIG. 6 shows a front view of a bifocal contact lens of the type that has different zones for near vision and far vision and requires a translation of the lens to place each zone in front of the entrance pupil of the eye. 1 shows a cross-sectional view of one embodiment of a contact lens of the present invention (peripheral and blend zones not shown). Sectional drawing of the 2nd embodiment of the contact lens of this invention is shown. FIG. 6 shows a “compound eye” shape (cross section) used in a possible bistable lens design configuration that represents the superposition of two different orientations of the eye relative to the lens. The eyes are shown in three different orientations (relative to the lens): front (7a), rotate up (7b) and rotate down (7c). Two possibilities of superposition for two eye shapes: superposition where the cornea overlaps and is truncated (8a) and superposition where the cornea does not overlap (8b). Figure 3 shows three zones used to create one possible bistable lens design. The “2 dimple” lens shape is shown. The blend zone of a “2 dimple” lens is shown. A cut-away view of a “2 dimple” lens design is shown. Figure 2 shows a cross section of a composite lens design in which the back surface is straightened in several areas to form a single concave surface.

Claims (18)

A contact lens having a near vision portion and a far vision portion, the first position corresponding to aligning the wearer's gaze through the near vision portion on the eye and the wearer's gaze in the far vision Can be moved between a second position corresponding to alignment through the part, positionally stable on the eye at each of the positions, the first position and the second position, A contact lens that requires a force to move between.   The contact lens of claim 1, having a back surface and a front surface, the back surface having one or two main back curve zones that occupy a major portion of the lens back surface.   The contact lens according to claim 2, wherein the main parts together constitute at least 50% of the back surface.   The contact lens of claim 3, wherein a peripheral edge of the lens does not form part of the main back curve zone.   The contact lens according to claim 2, wherein the back surface is defined by an important and non-critical concave surface.   The contact lens of claim 5, wherein the back surface includes a blend zone that folds well with these concave surfaces.   The contact lens according to claim 2, wherein a shape of the back surface is adapted to a continuous second derivative.   The contact lens according to claim 7, wherein a shape of the back surface is adapted to an infinite continuous differentiable function.   At least the center of the rear surface of the lens includes a concave surface or a combination of two concave surfaces, and any two points on any such concave surface are connected by a straight line that does not pass through the interior of the lens between those points. The contact lens according to claim 2.   The contact lens according to claim 9, wherein the concave surface covers the entire back surface of the lens except its peripheral edge.   The contact lens of claim 5, wherein the surface is combined with a narrow blend zone to achieve continuity at their junction.   If the lens is positionally more stable at one position than the other, and therefore is moved from a relatively stable position to a relatively unstable position, the lens is moved in reverse. The contact lens according to claim 1, which requires a larger force than the case.   The contact lens according to claim 1, wherein the lens is adapted to change a cross-sectional shape as it moves between the first position and the second position.   The contact lens of claim 13, wherein partial reversal of the lens occurs during the change in cross-sectional shape. A method of manufacturing a soft contact lens having a near vision portion and a far vision portion,
Defining an approximate first eye shape comprised of a spherical sclera and an elliptical cornea;
Rotating the first eye shape in a first direction to define a second eye shape;
Rotating the first eye shape in the opposite direction to define the second eye shape;
Superposing the second shape and the third shape to define a fourth eye shape;
Designing a soft lens having a back surface adapted to fit the fourth eye shape.   The rotation occurs about the center of the scleral sphere such that the first direction rotates the cornea up and the second direction rotates the cornea down, the first direction and second 16. The method of claim 15, wherein the distance of rotation away from horizontal in the direction of is approximately half of the translation distance required for the lens.   A lens substantially as herein described with reference to any one of the embodiments shown in the drawings.   A method of making a soft contact lens substantially as described and exemplified herein.

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